Nick Clegg is ahead on points — now tune in to the fightback

Round two: the party leaders leave the stage at the end of last week's TV debate

Is Nick Clegg the new Barack Obama? Only in the sense that I am the new Gwyneth Paltrow.

The comparison answers itself. Still, Cleggmania is the most important thing to have happened in this campaign, because it has so badly shaken the other parties out of their default mode, stupid posters and over-reliance on pictures of their wives in smart dresses.

A 10-point poll advance by what my children call "the little party who never win" has unleashed a week of frantic reconsidering in the two main parties' war counsels.

For Gordon Brown, no amount of saying "I agree with Nick Clegg" to attract Lib-Dem voters has compensated for the fact that the Cleggster plucked the heartstrings of disaffected voters more effectively than a Prime Minister who prides himself on his hackneyed language of "values" and expects us to fall in with his self-praise.

A huge historical irony attends Mr Brown's current overtures to the Lib-Dems, expressed through a last-minute embrace of (some) voting reform. For as long as anyone can remember, he has treated the third party with contempt. As a senior source puts it, "Blair at least did us the courtesy of messing around with us. Brown just ignored us."

The only senior characters in Labour who have any natural empathy with the Lib-Dems are former Blairites like Lord Adonis — a graduate of the SDP — and Peter Mandelson, who was close to the late Roy Jenkins, its founder, and involved in Mr Blair's early footsie with a "progressive consensus".

It is rather late now to begin a charm offensive but this is what Mr Brown must surely do. His dismissive tone to the third party down the years has rankled — hence the overcompensation in the last debate.

Tomorrow, when the first half of the event will be about foreign affairs, he cannot repeat this trick: his foreign policy (adherence to the Trident programme and a continuation of Blairite commitments abroad) contrasts sharply with the Lib-Dem habit of not being too keen on any foreign entanglement by Britain, quite apart from holding different views on the EU.

That is an Achilles heel for Mr Clegg, who has fallen in too lazily behind the Lisbon Treaty and forsaken his earlier more testing tone towards the EU (he would also have had us in the euro and thus even more bankrupt than we currently are).

In another suspect area of the Lib-Dem manifesto, he is keen on "free schools" but illogically suspicious of anyone being paid to run them well and downright destructive of high-performing faith schools: a foolish adjunct to appease his own Left wing. Mr Brown is also in a weak position here, having presided over a retreat from schools' independence in the state sector.

If Labour is worried about the debates, the mood in Camp Cameron is even jumpier.

The pressure on David Cameron personally is intense. He has long been the stand-out asset of the New Conservative Party. Only the slavish would say that he was not outmanoeuvred by the wide-eyed frankness of Nick Clegg, who has perfected the newly desirable image of "Stealth Posh".

The worst thing about the Clegg advance from Dave's perspective is that it projects another youngish, pleasant-looking bloke to contrast with the crumpled heap of overweening certainty that is Gordon.

Mr Cameron was already carrying a huge burden of expectation in this campaign: nervy strategists have sought to keep George Osborne out of the way, for fear of suggesting a rarefied duumvirate, like two characters out of Laura Wade's Royal Court satire Posh.

I do think, though, that Dave is at his best when he is on the back foot. He is a good learner: something Mr Brown has long forgotten. The Tory leader too has his troubles on Europe, but he has been adept in making them too boring or convoluted for the voters to care much about.

Otherwise, he has played a cautious hand on foreign policy under the tutelage of William Hague, backing key decisions by the Government like staying in Afghanistan, but picking up on weaknesses in execution.

It was no coincidence that his final Prime Minister's Questions began with an assault on the PM over lack of helicopters and the funding of the war: easy targets until you control the decisions about resources — and the finances.

In this inverted reality (one poll today makes Mr Clegg the next Prime Minister), the Tory leader cannot afford to play safe. His flabbiest suit has always been foreign policy: now he must make it the scene of his fightback.

In so doing, he must beware the siren advice of many instinctive supporters who think the whole Clegg adoration thing is an illogical spasm.

It may be: but only because the Conservative leader suffered in comparison with him on TV — and showed how fragile the electorate's attachment to the New Tories really is. They are still ill served by a front bench which, with the exceptions of George Osborne and Michael Gove, does not credibly project a new start.

If I were Dave, I would slam the door at home shouting: "God, do I have to do everything round here?" A longer look at the fissiparous Lib-Dems will, of course, give ample ammunition but too much negativity robs Mr Cameron of his claim to be the candidate of optimistic renewal. It is, as one senior aide confides: "the hardest strategic challenge we've faced — because we didn't see it coming".

Consider the impact of a Lib-Dem advance in the key marginals. It would hit a good number of the Tories Mr Cameron has cultivated as his new breed. A 20-seat advance could kill off Mr Cameron's allies Jesse Norman, Zac Goldsmith, Annunziata Rees-Mogg and that prize beast, the flexible ideologist, Oliver Letwin.

It all depends, however, on how Mr Clegg, who has lived within the sheltered walls of the Lib-Dem convent, copes with entering the second debate as the man with everything to lose.

Say what you like about the 2010 election, it isn't boring. And thank Nick for that.